Hi there
In regard to cc and class and
Bore and stroke changes
I presume that it's ok to alter / change or manipulate the engine bore and stroke to satisfy the particular class entered into
And therefore I presume I can alter inlet valves and manifolds and carbs to suit those mods..??..?yes
And what about the 50thou over how does that work
So does this mean I can have 650 cc plus a 50 thou oversize ?.. Please help
Rob

Rob
On a vintage class engine you can have up to .050" oversize and it will still be considered a std bore.
This is because most vintage blocks/cylinders have already been bored once or twice (or even more) and as new replacements may be unobtainable it means you don't have to resleeve back to std everytime you use another block/cylinder.
Cheers Mossy

arby wrote:So does this mean I can have 650 cc plus a 50 thou oversize ?.. Please help

Been waiting for that question ..
Mossy I think what Rob is trying to ask is .......... The 33/3 discount from 650cc puts me at 443cc which then
puts me in 500 class , from there can I bore the engine the 50thou available tolerance which will take back over 500cc,
which then puts me back in 650 class.... confused

Rob Is aiming at taking every available gift.. and so he should and I don't know the answer
Grumm may have come across this one before...
Mal will most probably know the right answer .. but wait for the wrong one before he shoots us down..

SO... My parting words with this one is..... I'm with you's blokes...

Ross...

PS. Rob .... Manipulate the internals anyway you like, just make sure it stays a flat head..

hi there
mmm,,,, thats my prob now,,, im not sure what i should be asking???
but believe me, my flat head needs all the help it can get,,,,
as long as i can run in the 500 class,,, and the motor ends up as big as im allowed,,, it matters not,,

i have bit of time before we start to prep the motor,,,,, so i will wait for the answer
thanks rob

I'm confused
What are you planning to do?
Lets have a look at the rule

7.J.10 Class VG and VF:
Same as Class G or F, except that the class is limited to motorcycle engines produced prior to 1956.
For reasons of historical authenticity, vintage engine modifications are restricted to older technology
levels as far as practical. Accordingly, in classes VF, VG, VBF and VBG newer technologies such as EFI,
or electronic reactive ignition systems are not in keeping with the spirit of the Vintage classes and are not
allowed. Computers are allowed for data collection purposes only.
Engines shall utilize OEM crankcase, OEM cylinders on flatheads and two strokes and OEM heads on
OHV engines. Above components made after 1955 and exact reproductions may be considered legal in
Vintage classes if they offer no competitive advantage. Pre installation approval by the contest board is
required. It is the entrant’s responsibility to provide documentation and samples. A .050 in. overbore is
allowed on vintage engines only (including production vintage) and will be discounted when the bore size
is measured.
Flathead engine displacement will be discounted 33 1/3% in determining engine displacement class
limits. For example, a 1500cc measured displacement would run as a 1000cc.

I'm drawn to OEM

In the new SCTA rulebook they have added a clarification

A .050 in. overbore is allowed on vintage engines only (including production vintage) only if the OEM bore diameter is within .050 in. (1.27mm) of maximum class displacement and will be discounted when the bore size is measured..

So I guess you can do what you want, however, if you are using a non OEM cylinder it must fit in the class capacity you are entered and then you get a 33% discount
If you are using an OEM cylinder, you can have a .050in overbore

The main thing to remember is, the same rules apply to everyone else who is running in vintage.
and if you are planning to run in a production class, make sure you send me pictures first, because we have a lot to talk about

Oh, and there will be no tolerance for any safety items next year. Right Ross

ok
the oem has got me thinking,,, this is where my issue is, and i thinks im in trouble
atm the motor is a standard issue 500cc side valve flat head 1941/2 army issue,, ie 741 scout
top speed maybe 50 with a tail wind down a hill, not fast nor quick and a very poor state of tune
if i wanted to fast and quick i could go out buy a fast and quick bike etc etc etc
however,,, i have a bike laying around thats needs work so i thought i would use the one i have
and id like to see the dear little thing get up to a respectable mph,,, what ever that is depends on the cc and mods allowable
so
i will ask again,,,,, its 500cc,,,, i want it to be 650cc is that allowed,, now im thinking not
most people bore them out to 600 and then mod the internals or change the cylinders ie sports scout 750cc

Rob
If its a 500 sv now, you can run it in the 350cc class. 500cc minus 33 1/3% = 333cc.

It would seem, going by our current rules, that you could bore it out .050" and still run in the 350cc class?? as the over bore is ignored on oem vintage barrels.

However if I'm reading the new SCTA rule correctly, a .050" over bore may take actual displacement over 350cc, in which case you would then be in the 500cc class.
If you Bore it out to 600cc you'll still be able to run the 500cc class because being a SV you'll be classified as 400cc. You can go up to 750cc and still run in the 500cc class.

I'm not sure why you want to run in the 650cc class when you can run in the 350cc or 500cc class???

Especially as in the M/VG 650 class you'll be up against me, and its unlikely an old SV Indian is ever going to outpace a 650 Triumph

So Grumm, Does this rule then mean that a .050 overbore on a 649cc engine will then be classifies as a 750, as the original size was `Not within .050"' of the max displacement for the class. If this is the case then it would seem the .050" allowance on vintage engines is pointless? Or is the .050" only allowed in Production class?

Hi there thanks for the reply
what is your top end on the trumpy,, you may be correct
My idea was to bore it out to 650 plus or minus the 50thou
So I could run in the 500 cc class
I'm sure,,,,, if I were to run a bigger motor I may have a chance at getting close,,, to you ,,,but that's probably another time
Rob

G'day Rob
This year was the first time racing on the salt for me and the bike.
Its reasonably standard at this stage, just bolt on performance mods. The best speed I did was on the GPS track where I managed 108mph.
So I was very happy with that.
Cheers Mossy